Human immunodeficiency virus type 1 (HIV-1), is the causative agent of acquired immunodeficiency syndrome (AIDS). This virus encodes a number of auxiliary proteins, Nef, Vif, Vpr, and Vpu, in addition to other retroviral proteins. While HIV-1 Nef is undoubtably an important factor responsible for HIV-1 pathogenesis, its function remains controversial. The nef gene of HIV-1 has been expressed in the yeast, S. cerevisiae to produce native Nef proteins (Macreadie et al., 1993). This protein is also released from the cell under certain stress conditions. Preliminary results using immunofluorescence have shown that the Nef protein is localized within the cell, yet high resolution information about its location is not known. We are using high pressure freezing followed by freeze substitution as a means of obtaining maximally preserved samples. These samples will be immunolabled to identify the location of Nef proteins in yeast under several growth conditions. By observing Nef in yeast, we hope to gain further insights into the development of AIDS.